This new version of the TimeTree web, a substantial update to the original created in 2009, not only includes colorful and clear visualizations of the divergence of different species across time, but also charts the atmospheric conditions and other “abiological” events that may have influenced the formation of new species.
“Oxygen levels, solar radiation, asteroid impacts — evolutionary biologists for years have looked at how the environment has affected life through time," Hedges told Seeker. "Here we have it all laid out."
One interesting example is the spike in oxygen levels that occurred during the Paleozoic era. That hyper-oxygenated air is believed to be responsible for the huge insects that roamed the Earth, like dragonflies the size of seagulls.
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If you go to the TimeTree web and search for “insecta” in the field that says “Build a TimeTree,” you can make an interesting correlation. As oxygen levels crested over the course of 150 million years, you see a related cluster of divergences over the same time period that created entire new orders of insects. After the oxygen spike flattened out about 200 million years ago, no new orders were born.
Not all environmental correlations are so easy. For example, biologists expected to see a big branching out of mammals after the Chicxulub asteroid impact that wiped out the dinosaurs 65 million years ago. But aside from elephants, manatees, koalas and some moles — all of which diverged soon after the event — most mammal appear to have evolved over the 100 million-year period before the asteroid crashed to Earth.
“These small mammals were scurrying under the feet of dinosaurs,” Hedges said.